Aerobic bacterial metabolism of phytol in seawater: effect of particle association on an abiotic intermediate step and its biogeochemical consequences

The biodegradation of phytol by a bacterial community isolated from the oxic zone of a Recent temperate marine sediment was studied in the presence, and in the absence, of a solid support. Analyses of isoprenoid wax esters produced by condensation of bacterial metabolites with themselves, or with phytol, showed that bacterial metabolism of phytol was strongly modified in the presence of the solid support. Aerobic metabolism of phytol involves the transient production of (E)-phytenal, which in turn can be quickly abiotically converted to 6,10,14-trimethylpentadecan-2-one or (E)-phytenic acid. Sorption on mineral particles appears to hinder the addition of water to the activated double bond of (E)-phytenal, which constitutes the first step of its transformation to the C18 isoprenoid ketone. Consequently, it is concluded that in surface temperate sediments phytol must be metabolised mainly via (E)-phytenic acid and that results obtained from in vitro experiments with free cell cultures may not be comparable to processes occuring in marine sedimentary environments.